Electric drive systems have been commonly used for large vehicles or stationary equipment. However, as the output/input speed ratio increases, the electric motor & generator no longer operate at their optimum operating speeds. This reduces the overall efficiency of the drive at the upper half of the drive's operating range. This problem may be overcome by having multiple gear settings to keep the motors and generators operating at or near their optimum speeds, but the complexity of the resulting transmission negates the benefits of using an electric drive.
An alternative to an electric drive system is a mechanically driven system. However, conventional mechanical drive systems are limited to discrete gear ratios, which do not allow for infinite speed ratios as found in electric drives. A great deal of power management between the engine and the transmission at all output speeds is necessary for transmission effectiveness. A purely mechanical drive is inadequate to ensure the efficient use of the engine's available power due to the discrete speed ratios, while a purely electric drive has inherently lower efficiency at higher operational speeds.
With the increasing costs of fuel and more stringent emissions requirements, there is a need for more efficient drive systems for large and small vehicles, as well as stationary equipment, to replace traditional electric and mechanical drive systems.
It is an object of this invention to provide a more efficient drive system for large and small vehicles and stationary equipment by combining electric and mechanical power systems. It is a further object of this invention to provide a transmission system for optimizing use of combined drive systems.